What is laser radiation? Laser radiation: its sources and protection from it

Lasers are becoming increasingly important research tools in the fields of medicine, physics, chemistry, geology, biology and technology. If used improperly, they can dazzle and cause injuries (including burns and electric injuries) to operators and other personnel, including random visitors to the laboratory, and cause significant damage to property. Users of these devices must fully understand and apply the necessary security measures when handling them.

What is a laser?

The word "laser" (English LASER, Light Amplification by Stimulated Emission of Radiation) is an abbreviation, which stands for "amplification of light by induced radiation". The frequency of radiation generated by the laser is within or near the visible part of the electromagnetic spectrum. Energy is amplified to a state of extremely high intensity through a process called "laser induced radiation."

The term "radiation" is often misunderstood, because it is also used to describe radioactive materials. In this context, it means the transfer of energy. Energy is transferred from one place to another by means of conductivity, convection and radiation.

There are many different types of lasers working in different environments. Gases (for example, argon or a mixture of helium with neon), solid crystals (for example, ruby) or liquid dyes are used as a working medium. When energy is supplied to the working medium, it passes into an excited state and releases energy in the form of light particles (photons).

A pair of mirrors at both ends of the sealed tube either reflects or transmits light in the form of a concentrated stream called a laser beam. Each working environment produces a beam of unique wavelength and color.

The color of laser light, as a rule, is expressed by the wavelength. It is non-ionizing and includes ultraviolet (100-400 nm), visible (400-700 nm) and infrared (700 nm - 1 mm) part of the spectrum.

Electromagnetic spectrum

Each electromagnetic wave has a unique frequency and length associated with this parameter. Just as red light has its own frequency and wavelength, and all other colors - orange, yellow, green and blue - have unique frequencies and wavelengths. People are able to perceive these electromagnetic waves, but they can not see the rest of the spectrum.

The greatest frequency is gamma rays, X-rays and ultraviolet. Infrared, microwave radiation and radio waves occupy the lower frequencies of the spectrum. Visible light is in a very narrow range between them.

Laser radiation: effects on humans

The laser produces an intense directional beam of light. If it is directed, reflected or focused on the object, the beam is partially absorbed, raising the temperature of the surface and the inside of the object, which can cause a change or deformation of the material. These qualities, which have found application in laser surgery and material processing, can be dangerous for human tissues.

In addition to radiation, which has a thermal effect on tissues, laser radiation, which produces a photochemical effect, is dangerous. Its condition is a sufficiently short wavelength, i.e., the ultraviolet or blue part of the spectrum. Modern devices produce laser radiation, the effect on a human being is minimized. The energy of low-power lasers is not enough to cause harm, and they do not represent a danger.

Human tissues are sensitive to the effects of energy, and under certain circumstances, electromagnetic radiation, laser radiation, including, can lead to damage to the eyes and skin. Threshold levels of traumatic radiation were studied.

Danger to the eyes

The human eye is more prone to injury than the skin. The cornea (the transparent outer front surface of the eye), unlike the dermis, does not have an outer layer of dead cells protecting from the environment. Laser and ultraviolet radiation is absorbed by the cornea of the eye, which can harm it. Trauma is accompanied by edema of the epithelium and erosion, and in severe injuries - opacification of the anterior chamber.

The lens of the eye can also be prone to injury when it is affected by a variety of laser radiation - infrared and ultraviolet.

The greatest danger, however, is the effect of the laser on the retina in the visible part of the optical spectrum - from 400 nm (violet) to 1400 nm (near infrared). Within this region of the spectrum, collimated rays are focused on very small areas of the retina. The most unfavorable variant of the effect occurs when the eye looks afar and a direct or reflected ray enters it. In this case, its concentration on the retina reaches 100 000 times.

Thus, a visible beam with a power of 10 mW / cm ² acts on the retina of the eye with a power of 1000 W / cm ² . This is more than enough to cause damage. If the eye does not look into the distance, or if the ray reflects from a diffuse, non-mirror surface, much more powerful radiation leads to trauma. Laser impact on the skin is devoid of the effect of focusing, so it is much less susceptible to injury at these wavelengths.

X-rays

Some high-voltage systems with a voltage of more than 15 kV can generate X-rays of considerable power: laser radiation, whose sources are powerful excimer lasers with electron pumping, as well as plasma systems and ion sources. These devices must be checked for radiation safety, including to ensure proper shielding.

Classification

Depending on the power or energy of the beam and the wavelength of the radiation, lasers are divided into several classes. Classification is based on the potential ability of the device to cause immediate injury to the eyes, skin, inflammation with direct exposure to the beam or when reflected from diffuse reflective surfaces. All commercial lasers are to be identified with the help of labels placed on them. If the device has been manufactured at home or not otherwise marked, advice should be obtained on the appropriate classification and labeling. Lasers are distinguished by power, wavelength and exposure time.

Secure devices

The devices of the first class generate low-intensity laser radiation. It can not reach a dangerous level, so the sources are exempt from most control measures or other forms of surveillance. Example: laser printers and CD players.

Conditionally safe devices

Lasers of the second class radiate in the visible part of the spectrum. This is laser radiation, the sources of which cause a normal reaction in the person of rejection of too bright light (blinking reflex). When exposed to a beam, the human eye blinks after 0.25 seconds, which provides sufficient protection. However, laser radiation in the visible range can damage the eye at constant exposure. Examples: laser pointers, geodesic lasers.

The 2a-class lasers are special-purpose devices with an output power of less than 1 mW. These devices cause damage only with direct exposure for more than 1000 s for an 8-hour day. Example: bar code readers.

Dangerous lasers

Class 3a refers to devices that do not injure a short-term exposure to an unprotected eye. Can be dangerous when using focusing optics, for example, telescopes, microscopes or binoculars. Examples: 1-5 mW helium-neon laser, some laser pointers and building levels.

A class 3b laser beam can cause injury when exposed to direct light or when it is reflected in a mirror. Example: helium-neon laser power of 5-500 mW, many research and therapeutic lasers.

Class 4 includes devices with power levels of more than 500 mW. They are dangerous to the eyes, skin, and fire. Influence of the beam, its mirror or diffuse reflections can cause eye and skin injuries. All security measures must be taken. Example: Nd: YAG-lasers, displays, surgery, metal cutting.

Laser radiation: protection

Each laboratory should provide adequate protection for persons working with lasers. Windows of rooms through which radiation from Class 2, Class 3 or Class 4 devices can be harmed in uncontrolled areas, should be covered or otherwise protected during operation of such a device. To ensure maximum eye protection, the following is recommended.

• The bundle must be encapsulated in a non-reflective non-flammable protective shell in order to minimize the risk of accidental exposure or fire. For aligning the beam, use fluorescent screens or secondary viewers; Avoid direct exposure to the eyes.
• For the beam alignment procedure, use the lowest power. If possible, use low-end devices for preliminary alignment procedures. Avoid the presence of unnecessary reflecting objects in the laser working area.
• Limit the passage of the beam in a hazardous area during non-working hours, using dampers and other obstructions. Do not use the walls of the room to equalize the beam of Class 3b and 4 lasers.
• Use non-reflective tools. Some inventory that does not reflect visible light becomes mirror in the invisible region of the spectrum.
• Do not wear reflective jewelry. Metal ornaments also increase the risk of electric shock.

Protective glasses

When working with Class 4 lasers with an open hazardous area or with a risk of reflection, protective eyewear should be used. Their type depends on the type of radiation. Points should be chosen to protect against reflections, especially diffuse, and to provide protection to a level where a natural protective reflex can prevent eye injuries. Such optical devices will retain some visibility of the beam, prevent skin burns, reduce the possibility of other accidents.

Factors to consider when choosing safety glasses:

• Wavelength or region of the radiation spectrum;
• Optical density at a certain wavelength;
• Maximum illumination (W / cm ² ) or beam power (W);
• Type of laser system;
• Power mode - pulsed laser radiation or continuous mode;
• The possibility of reflection - mirror and diffuse;
• line of sight;
• The presence of corrective lenses or a sufficient size, allowing wearing glasses for correcting vision;
• comfort;
• The presence of ventilation holes, preventing fogging;
• Influence on color vision;
• Impact resistance;
• The ability to perform the necessary tasks.

Since the goggles are prone to damage and wear, the laboratory safety program must include periodic checks of these protective elements.